1. Field of the Invention
The invention relates generally to the field of devices and methods for obtaining samples (cores) of subsurface Earth formations during the drilling of wellbores. More specifically, the invention relates to coring devices and methods that use high speed data and control signal telemetry to improve the efficiency of core recovery.
2. Background Art
During drilling of wellbores through subsurface Earth formations, it is known in the alt to drill samples of such formations for recovery from the wellbore and subsequent analysis at the surface. Such sample taking is referred to as “coring.” Coring typically includes drilling the wellbore using an annular drill bit, such that a substantially cylindrical sample of the formation is moved into a recovery chamber or “barrel” during the coring operation. It is desirable to maintain environmental conditions in the sample as close as is practicable to those existing in the subsurface at the depth of the core sample so that an accurate analysis of the fluid content, mineral composition and fluid transport properties of the sample may be made. Various devices are known in the art for maintaining such conditions and for making measurements of various physical parameters on the sample during its acquisition. One such device is disclosed in U.S. Pat. No. 5,984,023 issued to Sharma et al.
A limitation common to all coring techniques and devices known in the art is that they rely in indirect indicators to inform the wellbore operator as to the status of the core sampling operation. For example, it is necessary to infer that the entire core sample chamber (“core barrel”) has been filled with a core sample by having drilled a length of the wellbore that is substantially equal to the axial length of the core barrel. It is not possible, using techniques known in the art, to determine whether the core barrel is in fact full of core sample without retrieval of the core drilling tool assembly from the wellbore. Further, it is not possible to be assured of the quality of a particular core sample, or that the core sample has even been retained in the core barrel, during retrieval of the core drilling tool assembly from the wellbore. All of the foregoing limitations can result in costly, inefficient coring operations.
Recently, a type of drill pipe (“wired drill pipe”) that enables transmission of electrical power and/or electrical signals along a drilling tool assembly has been developed. One example of such wired drill pipe is disclosed in U.S. Patent Application Publication No. 2006/0225926 filed by Madhavan et al. and assigned to the assignee of the present invention. Such wired drill pipe has been adapted to transmit, substantially in real time to the surface measurements made of various properties of the subsurface formations. While such measurements are quite useful, they cannot entirely replace analysis of actual samples of the subsurface formations in order to accurately evaluate properties of subsurface oil, gas and/or water reservoirs.
There continues to be a need for improved coring devices and methods that better assure core recovery and core condition.